Refrigeration & Air-Conditioning Practice Set-3

May 18, 2021

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1. The C.O.P. of a refrigerator working on a reversed Carnot cycle is (where T₁ = Lowest absolute temperature, and T₂ = Highest absolute temperature)

(T₁ - T₂)/T₁

(T₂ - T₁)/T₁

T₂/ (T₂ - T₁)

T₁ / (T₂ - T₁)

2. Which of the following cycles uses air as the refrigerant?

Ericson

Stirling

Bell Coleman

Carnot

3. The general rule for rating refrigeration systems (excepting for CO₂ system) is to approximate following h.p. per ton of refrigeration

0.1 to 0.5 h.p. per ton of refrigeration

0.5 to 0.8 h.p. per ton of refrigeration

2 to 5 h.p. per ton of refrigeration

1 to 2 h.p. per ton of refrigeration

4. Critical temperature is the temperature above which

A gas will never liquefy

Water will never evaporate

Water will evaporate

A gas will immediately liquefy

5. Rating of a domestic refrigerator is of the order of

0.1 ton

40 tons

10 tons

5 tons

6. The vapour compression refrigerator employs the following cycle

Carnot

Rankine

Reversed Rankine

Reversed Carnot

7. The domestic refrigerator uses following type of compressor

Miniature sealed unit

Axial

Piston type reciprocating

Centrifugal

8. A certain refrigerating system has a normal operating suction pressure of 10 kg/cm gauge and condensing pressure of about 67 kg/cm. The refrigerant used is

Freon

Brine

Carbon dioxide

Ammonia

9. The value of C.O.P in vapour compression cycle is usually

Any one of the above

Equal to unity

Always more than unity

Always less than unity

10. Most thermostatic expansion valves are set for a superheat of

10°C

20°C

15°C

5°C

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11. The change in evaporator temperature in a refrigeration cycle, as compared to change in condenser temperature, influences the value of C.O.P.

Equally

Unpredictable

Less

12. A reversible engine has ideal thermal efficiency of 30%. When it is used as a refrigerating machine with all other conditions unchanged, the coefficient of performance will be

2.33

1.33

3.33

4.33

13. In a flooded evaporator refrigerator, an accumulator at suction of compressor is used to

Collect vapours

Superheat the vapour

Collect liquid refrigerant and prevent it from going to compressor

Detect liquid in vapour

14. Cooling water is required for following equipment in ammonia absorption plant

Evaporator

Condenser

Condenser, absorber and separator (rectifier)

Absorber

15. On the pressure-enthalpy diagram, condensation and desuperheating is represented by a horizontal line because the process

Takes place at constant entropy

Involves no change in volume

Takes place at constant temperature

Takes place at constant pressure

16. Freon group of refrigerants are

Nontoxic and non-inflammable

Non-inflammable and toxic

Inflammable

Toxic

17. The curved lines on a psychrometric chart indicates

Dry bulb temperature

Wet bulb temperature

Dew point temperature

Relative humidity

18. In a lithium bromide absorption refrigeration system

Ammonia is used as a refrigerant and lithium bromide as an absorbent

None of these

Lithium bromide is used as a refrigerant and water as an absorbent

Water is used as a refrigerant and lithium bromide as an absorbent

19. Mass flow ratio of NH₃ in comparison to Freon-12 for same refrigeration load and same temperature limits is of the order of

1: 1

1: 3

1: 9

9: 1

20. For obtaining high COP, the pressure range of compressor should be

Any value

High

Low

Optimum

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21. The atmospheric air at dry bulb temperature of 15°C enters a heating coil maintained at 40°C. The air leaves the heating coil at 25°C. The bypass factor of the heating coil is

0.67

0.4

0.376

0.6

22. In a refrigeration system, heat absorbed in comparison to heat rejected is

Same

More for small capacity and less for high capacity

Less

23. The condition of refrigerant after passing through the condenser in a vapour compression system is

Superheated vapour

Dry saturated vapour

Saturated liquid

Wet vapour

24. A bootstrap air cooling system has

One heat exchanger

Two heat exchangers

Three heat exchangers

Four heat exchangers

25. The operating pressure for refrigerating units using R-12 as a refrigerant is

30 bar

8 bar

15 bar

2 bar

26. The minimum temperature to which water can be cooled in a cooling tower is

Dry bulb temperature of air

Ambient air temperature

Wet bulb temperature of air

Dew point temperature of air

27. A human body feels comfortable when the heat produced by the metabolism of human body is equal to the

(A) Heat dissipated to the surroundings

(D) Difference of (A) and (B)

(B) Heat stored in the human body

28. The bank of tubes at the back of domestic refrigerator is

Capillary tubes

Refrigerant cooling tubes

Condenser tubes

Evaporator tubes

29. When the temperature of the surrounding is higher than the temperature of the body, then the heat loss by convection from the body to the surrounding will be

None of these

Zero

Positive

Negative

30. In actual air-conditioning applications for R-12 and R-22, and operating at a condenser temperature of 40° C and an evaporator temperature of 5° C, the heat rejection factor is about

5.12

1.25

2.15

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31. In a refrigeration system, the expansion device is connected between the

Evaporator and compressor

Condenser and receiver

Receiver and evaporator

Compressor and condenser

32. The boiling point of ammonia is

-33.3°C

-10.5°C

-30°C

-77.7°C

33. The refrigerant after condensation process is cooled below the saturation temperature before throttling. Such a process is called

None of these

Super-cooling

Normal cooling

Sub-cooling or under-cooling

34. A thermostatic expansion valve in a refrigeration system

None of the above

Ensures the evaporator completely filled with refrigerant of the load

Maintains different temperatures in evaporator in proportion to load

Is suitable only for constant load systems

35. Which of the following statement is correct?

(D) Both (A) and (B)

(B) The increase in air movement increases the evaporation from the human body.

(A) The human body can lose heat even if its temperature is less than the atmospheric temperature.

36. Highest temperature encountered in refrigeration cycle should be

At critical Temperature

Much below critical temperature

Above critical temperature

Near critical temperature of refrigerant

37. If a heat pump cycle operates between the condenser temperature of +27°C and evaporator temperature of -23°C, then the Carnot COP will be

1.2

0.2

38. The capillary tube, as an expansion device, is used in

Room air conditioners

Domestic refrigerators

Water coolers

All of these

39. Which of the following is not a desirable property of a refrigerant?

Large latent heat

Good electrical conductor

Low boiling point

High risibility with oil

40. The freezing point of sulphur dioxide is

-135.8°C

-77.7°C

-75.2°C

-56.6°C

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A Demrot is the founder of VideRime Online Learning, a leading engineering website. He did his BE Civil and M.Tech Structure from RGPV University, Bhopal and has been working as an Assistant Professor in a reputed college.

Refrigeration & Air-Conditioning Practice Set-3

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